re - SWXCR RAID interface
Digital 2100 Server Model A500MP DEC SWXCR
controller xcrn at * vector xcintr
device disk renn at xcrn drive nn
The re driver is for the SWXCR RAID Array controller.
The following rules are used to determine the major and minor numbers that are associated with an re type disk. There are two major numbers used to represent re disks. The major numbers are 11 for block devices and 44 for character (raw) devices.
The minor number is used to represent both the unit number and partition. A disk partition refers to a designated portion of the physical disk. To accomplish this reference, the 20-bit minor number is divided into three parts. The lowest six bits of the minor number specify a disk partition. The partitions use a letter, a through h, for their name.
The next three bits of the minor number specify the RE unit number for a unit attached to an SWXCR controller. The final 11 bits specify the controller number.
The device special file names associated with re disks are based on conventions that are closely associated with the minor number assigned to the disk. The standard device names begin with re for block special files and rre for character (raw) special files. Following the re is the unit number and then a letter, a through h, that represents the partition. Throughout this reference page, the question mark (?) character represents the unit number in the name of the device special file. For example, re?b could represent re0b, re1b, and so on.
The unit number can be calculated if the major and minor numbers of an re disk are provided. For example, suppose you have a device special file rre6a, with a major number of 44 and a minor number of 384. The partition is represented by the lower six bits of the number 384. These lower six bits of the number 384 are 0, which specifies the a partition. The next three bits of the minor number 384 specify the unit number, which is 6. The next eleven bits specify the controller number, which is zero. Putting these three pieces together reveals that the major/minor number pair 44/384 refers to the a partition of unit 6 attached to controller number 0.
A disk can be accessed through either the block special file or the character special file. The block special file accesses the disk using the file system's normal buffering mechanism. Reads and writes to the block special file can specify any size. This capability avoids the need to limit data transfers to the size of physical disk records and to calculate offsets within disk records. The file system can break up large read and write requests into smaller fixed size transfers to the disk.
The character special file provides a raw interface that allows for direct transmission between the disk and the user's read or write buffer. A single read or write to the raw interface results in exactly one I/O operation. Consequently, raw I/O may be considerably more efficient for large transfers.
For systems with RE disks, the first software boot after the system is powered on may take longer than expected. This delay is normal and is caused by the software spinning up the RE disks.
SWXCR RAID Controllers are viewed in all cases as RE type disks. There are some notable differences that should be taken into consideration when configuring a RAID device: Currently only sector sizes of 512 bytes are supported. Logical Volume sizes are not fixed sizes as compared to other disk devices. The size of the Logical Volume is configurable based on needs. The dynamic nature of Logical Volume sizes is dealt with by defining RAID devices as DYNAMIC. Only partitions a, b, c, and g are defined. If necessary, the disklabel(8) command can be run to change and define partitions for RAID devices.
Usually, the re?a partition is used for the root file system and the re?b partition as a paging area. The re?c partition can be used for disk-to-disk copying because it maps the entire disk.
The starting location and length (in 512 byte sectors) of the disk partitions of each drive are shown in the following table. Partition sizes can be changed by using the disklabel(8) command.
SWXCR (RAID) partitions for systems
based on the Alpha AXP architecture
disk start length
re?a 0 131072
re?b 131072 262144
re?c 0 end of media
re?d 0 0
re?e 0 0
re?f 0 0
re?g 393216 end of media
re?h 0 0
/dev/re??? /dev/rre??? /etc/disktab
disklabel(8), MAKEDEV(8), uerf(8) delim off